570
Practical MATLAB
® Applications for Engineers
The OA is basically a voltage amplifi er with a large open-loop gain (about 10
6
), a
large input impedance (about 2 MΩ), and a small output impedance (about 75 Ω).
The symbol used to represent an OA as well as its typical electrical specs are indicated in Figure 6.5.
R.6.44 Digital fi lters, in contrast, use digital processors to perform numerical operations
on a sequence of discrete (sampled) values representing an analog signal.
The processor can be a powerful computer, a personal computer (PC), or a digital
signal processing (DSP) special chip.
Samplers, analog-to-digital converters and encoders, are used to convert and process the analog signal into a discrete signal.
This signal is then represented by a sequence of numbers that are stored and then
processed.
R.6.45 Some of the key features that distinguish digital from analog fi lters are summarized as follows:
Digital fi lters are programmable.
Digital fi lters are implemented using software packages.
Digital fi lters can easily be changed or updated without affecting their circuitry (hardware).
Digital fi lters can be designed, tested, and implemented on a general-purpose
computer.
Digital fi lters are independent of physical variables such as temperature, tolerances of elements, noise, fl uctuations, or interference.
Analog fi lters use elements that are environment dependent, and any fi lter
change is usually hard to implement and a complete redesign is often required.
R.6.46 Let us get back to the normalized passive fi rst-order fi lters. Some simple implementations of LPF are shown in Figure 6.6.
•
•
•
•
•
•
FIGURE 6.5
The operational amplifi er.
1
2
3
V i (w )
V o (w)
Z o
Z i
OA
Voltage gain = 200,000 (106 db)
Z o = 75 Ω
Z i = 2 MΩ
Output voltage swing = +13 V, −13 V
Small signal BW = 1 MHz
FIGURE 6.6
Normalized passive fi rst-order LPF.
R = 1 Ω
R = 1 Ω
C = 1 F
L = 1 H
V i (s)
V i (s)
V o (s)
V o (s)
H(s) =
V o (s)
V i (s)
= 1
s+1
The transfer function of either circuit is
CRC_47760_CH006.indd 570
CRC_47760_CH006.indd 570
7/23/2008 2:26:32 PM
7/23/2008 2:26:32 PM
Practical MATLAB
® Applications for Engineers
The OA is basically a voltage amplifi er with a large open-loop gain (about 10
6
), a
large input impedance (about 2 MΩ), and a small output impedance (about 75 Ω).
The symbol used to represent an OA as well as its typical electrical specs are indicated in Figure 6.5.
R.6.44 Digital fi lters, in contrast, use digital processors to perform numerical operations
on a sequence of discrete (sampled) values representing an analog signal.
The processor can be a powerful computer, a personal computer (PC), or a digital
signal processing (DSP) special chip.
Samplers, analog-to-digital converters and encoders, are used to convert and process the analog signal into a discrete signal.
This signal is then represented by a sequence of numbers that are stored and then
processed.
R.6.45 Some of the key features that distinguish digital from analog fi lters are summarized as follows:
Digital fi lters are programmable.
Digital fi lters are implemented using software packages.
Digital fi lters can easily be changed or updated without affecting their circuitry (hardware).
Digital fi lters can be designed, tested, and implemented on a general-purpose
computer.
Digital fi lters are independent of physical variables such as temperature, tolerances of elements, noise, fl uctuations, or interference.
Analog fi lters use elements that are environment dependent, and any fi lter
change is usually hard to implement and a complete redesign is often required.
R.6.46 Let us get back to the normalized passive fi rst-order fi lters. Some simple implementations of LPF are shown in Figure 6.6.
•
•
•
•
•
•
FIGURE 6.5
The operational amplifi er.
1
2
3
V i (w )
V o (w)
Z o
Z i
OA
Voltage gain = 200,000 (106 db)
Z o = 75 Ω
Z i = 2 MΩ
Output voltage swing = +13 V, −13 V
Small signal BW = 1 MHz
FIGURE 6.6
Normalized passive fi rst-order LPF.
R = 1 Ω
R = 1 Ω
C = 1 F
L = 1 H
V i (s)
V i (s)
V o (s)
V o (s)
H(s) =
V o (s)
V i (s)
= 1
s+1
The transfer function of either circuit is
CRC_47760_CH006.indd 570
CRC_47760_CH006.indd 570
7/23/2008 2:26:32 PM
7/23/2008 2:26:32 PM